This invention relates generally to digitally tuned television receivers and specifically to such receivers that incorporate tuning memories for a limited number of channels. The invention deals specifically with memory organization in receivers that are user programmable to receive desired channels at a limited number of tuning positions.
The prior art includes a variety of all-channel television receivers having a limited number of tuning positions, which are usually vertically oriented adjacent to the picture tube. Each position may be programmed to receive any of the 82 FCC allocated television channels by accessing the various positions and tuning in a desired channel at each position. Translucent channel number identification tabs, corresponding to the number of the tuned channel, are generally inserted adjacent to the tuning position. The receiver may be thereafter tuned either remotely or via an up/down switch with the position and channel member selected being set apart by being illuminated, for example. Some receivers incorporate push buttons at each tuning position and direct tuning to a programmed channel may be accomplished by pushing the appropriate button.
Each of these systems incorporates a memory having fewer locations than there are FCC allocated television channels. This represents a practical solution since only a very few of the 82 allocated channels are available in any given geographical area. To provide memory for every channel would not only prove cumbersome, but economically wasteful, since memory costs are a function of memory size or capacity and system complexity is related to the number of tuning positions. The larger the memory, whether in terms of number of words (locations) or length of words (bits), the greater the cost.
Most prior art systems incorporate memories in the form of potentiometers. There are also systems which use digital to analog converters for storing tuning voltage words, sometimes of considerable length. One proposed limited channel system is designed to store 14 bits of tuning information for each of 16 tuning positions. Some of the less obvious drawbacks of limited channel receivers are the difficulties presented to the user. Specifically, the viewer must often perform complicated programming operations and remember the programmed channels and their sequence.
With the invention, the viewer need not "keep track of" programmed channels or their sequence. It is done automatically. As will be seen, the viewer is also not normally aware of the fact that he has only a limited channel television receiver since he is not confronted with the channel position display, whether vertically oriented or in the form of a rotatable drum. Ease of programming and viewer operation are greatly enhanced. With prior art limited channel systems all programmed numbers or positions are visible in the sense that a multiple location display panel area or a rotatable drum is provided. In the inventive system, a display area need be provided for a single two digit channel number only, thus not only simplifying the system, enabling a larger more legible channel number readout, but also allowing a great deal of styling freedom to the designer.
The system has a programmed channel and a skipped channel mode. In the programmed channel mode, each entered channel number is automatically searched for among the limited locations of the memory and the system only stops at programmed channels. For these channels, tuning information exists in the tuning memory at a channel number identifiable address. Whenever that channel number is selected, the memory contents are read out for tuning the receiver to the "memorized" channel. Many advantages over prior art systems obtain with the memory organizing system of the invention. For example, the desired channels are read out in sequence without duplication. A viewer thus need not remember in what order the channels have been programmed not whether the channel has been programmed. The system automatically reads the programmed channels out in sequential order. If the desired channel number does not appear in this mode, that indicates to the viewer that the channel has not been programmed.
In the skipped channel mode, only unprogrammed channel numbers stop the system. The system reaches an unused memory location, if available. If no unused memory locations are available, the system will so indicate to the viewer. Thus should it be desired to program in a channel, the viewer need merely generate that channel number in the skipped channel mode which automatically accesses one of the unused memory locations. Should all memory locations be filled, the viewer is given a visual indication that further channels cannot be programmed in without removing a previously programmed channel. Thus the viewer needn't remember which channels have been programmed.